biology

• Population growth


  • Two types: Exponential growth and Logistic growth
  • Exponential growth starts slow and then accelerates rapidly, forming a J curve
  • Logistic growth starts similarly but levels off, forming an S curve
• Logistic growth

  Occurs due to limits to growth, represented by a carrying capacity where the population stops growing in size due to limited resources
• Exponential growth

  No limits to growth, continues to grow faster and faster infinitely
• In logistic growth, the limit is the carrying capacity, which is the level at which a population stops growing due to limited resources
• Exponential growth continues to grow faster and faster infinitely according to the model
• Most populations, especially invasive species, grow exponentially when resources are not limiting
• When a population first colonizes an area, it grows exponentially without limits until it starts approaching the carrying capacity limit
• Limits to growth

  • Food
  • Shelter
  • Disease
  • etc...
• Population growth

  Starts fast when far from limit, slows down as it approaches the limit, and halts when it reaches the carrying capacity
• Population growth fluctuates around the carrying capacity limit, with births and deaths balancing out to maintain a stable population size
• Population ecology


  Study of the factors that affect species’ populations and how and why a population changes over time
• Population


  Consists of all the organisms of a particular species living in a given area
• Exponential growth patterns of populations

  • Occur in ideal, unlimited environments
• Logistic growth pattern of populations

  • Occurs when environmental pressures slow the rate of growth
• Spatial distribution


  Describes how spread out a population is
• Population density

  Describes how many individuals are found in a given area
• Factors affecting population changes

  Age of organisms at first reproduction, frequency of reproduction, number of offspring produced, presence or absence of parental care, and reproductive lifespan
• Geographical range


  Preferred geographical range of a species dependent on ideal habitats
• Changes in geographical range

  Indicative of climate change and certain types of human activity such as the spread of invasive species
• Core populations

  Occur in the center of a geographical range
• Marginal populations


  Found at the boundary of the range and tend to be more at risk
• Ecological genetics


  Study of genetics in natural populations focusing on traits of ecological significance and fitness
• Ecological genetics


  Focuses on traits involved in interactions within and between species, and between organisms and their environment
• Life table in ecology
• Survivorship curves

  Plotting the number of individuals still alive at each age in a population
• Type I survivorship curve

  Reflects low juvenile mortality with most individuals living to old age
• Type II survivorship curve

  Constant probability of dying at any age
• Type III survivorship curve

  Reflective of high mortality among the young, flattening out as individuals reach maturity
• Age structure


  Composition of a population in terms of the proportions of individuals of different ages for a defined time
• Age structure and population status


  Indicator of population status, with growing populations having larger proportions of young individuals and stable populations having more individuals in reproductive-age classes
• Age structure and breeding dynamics


  Influence of male age structure on breeding dynamics in populations
• Types of population growth

  • Exponential and logistic
• Breeding periods tend to be longer and females typically breed later in the season
• Later breeding can lead to later birth dates which can lower juvenile survival, affecting a population’s ability to increase in numbers
• Types of population growth

  • Exponential
  • Logistic
• Exponential growth


  Unperturbed increase in population size when there are plentiful resources available, population keeps growing bigger and faster over time
• Logistic growth

  Influenced by limited resources in the environment, grows more slowly as it gets larger, eventually reaches carrying capacity
• Density in population


  Number of individuals per a given unit of area
• Delayed density dependence

  Population growth controlled by negative feedback operating with a time lag
• Ecologists have long been studying population cycles and haven’t been able to successfully explain them, delayed density dependence may hold the key